replace constexpr with const becasuse vs2013 lack of support

include/c11log/details/fast_oss.h

@@ -4,6 +4,7 @@
 // uses stack_buf as the underlying buffer (upto 192 bytes before using the heap)
 
 #include <ostream>
+#include <iomanip>
 #include "stack_buf.h"
 
 namespace c11log
@@ -13,8 +14,8 @@ namespace details
 
 class stack_devicebuf :public std::streambuf
 {
-public:    
-	static constexpr unsigned short stack_size = 192;
+public:
+    static const unsigned short stack_size = 192;
     using stackbuf_t = stack_buf<stack_size>;
 
     stack_devicebuf() = default;

include/c11log/details/line_logger.h

@@ -6,7 +6,6 @@
 #include "fast_oss.h"
 
 
-
 // line_logger class.
 // aggregates single log line (on the stack if possibe) and calls the logger upon destruction
 

include/c11log/details/stack_buf.h

@@ -17,7 +17,7 @@ class stack_buf
 public:
     using bufpair_t = std::pair<const char*, std::size_t>;
     using iterator = char const*;
-    static constexpr unsigned short stack_size = STACK_SIZE;
+    static const unsigned short stack_size = STACK_SIZE;
     stack_buf() :_v(), _stack_size(0) {}
     ~stack_buf() = default;